The present invention relates to a day/night rearview mirror. More specifically it relates to a day/night mirror in which an optical medium is electrically driven between transmissive and opaque states to impart the day/night characteristic to the mirror.
Day/night rearview mirrors are often used in automotive vehicles, particularly for the benefit of the driver so that at night he or she is not blinded by bright headlights from a trailing vehicle.
Known types of day/night rearview mirrors comprise mechanical operators for selectively positioning the mirrored surface depending upon prevailing conditions. Most of these are manually set by the driver to either one position for daytime use or another position for night use. For example, one way is by flipping a lever. It is also known to perform the repositioning automatically, for example by an electromechanical device.
Another class of day/night rearview mirrors comprises an optical transmission plate disposed in front of the mirrored reflecting surface. The optical transmission plate comprises a medium whose optical properties are controlled by the application of voltage to the medium. One particular type of transmission plate comprises a fluid medium disposed as a thin film between glass plates. When the medium is in its transmissive or non-opaque state, it does not attenuate light passing through it to any appreciable extent. This is the state which should be present for daytime operation so that maximum brightness of the reflected daylight scene is presented to the observer.
When the medium is operated to a less transmissive, or opaque state, it significantly attenuates light passing through it. Therefore, the brightness of the scene which is reflected to the observer is considerably less than for daytime operation; however, this nighttime mode of operation is to protect the observer from being blinded by headlights from a trailing vehicle.
Different types of media can be used, dichroics and nematics being examples of known fluid media. An individual medium has its own particular properties correlating the degree of opaqueness with the magnitude of applied voltage. For some media, this is a direct characteristic while for others it is an inverse characteristic. In other words in a direct characteristic, the medium has full light transmission at zero input voltage, and the opaqueness increases with increasing voltage up to a maximum opaqueness at and above a particular voltage. An inverse characteristic is just the opposite.
Mirrors embodying an optical transmission plate containing a medium which is electrically controlled to control brightness are desirable because mechanical actuators and mechanisms are not employed. Mechanical and electromechanical types of actuators and mechanisms have been deemed unacceptable to the original equipment automotive industry for various reasons, and one significant reason is that they have been unable to meet the rigorous demands which automobile manufacturers require for quality functional products.
The general idea of using an electrically controlled optical transmission plate in association with a rearview mirror is known.
The following patents are known. U.S. Pat. Nos. 3,280,701; 3,337,286; 4,299,444; 4,201,451; 3,862,798; 4,200,361; U.K. No. 2,029,343; and Fed. Rep. of Germany No. 2,808,260.
It is recognized in certain of these patents that a photocell sensing light from the rear can be used to automatically control the operation of the day/night mirror. Certain patents also show ambient sensors which attempt to distinguish between day and night conditions.
The present invention, in one respect, relates to a new and improved day/night mirror of the type in which the day/night operation is controlled by control of the voltage applied to a medium whose optical properties are related to voltage.
In order to achieve acceptable modes of operation in a day/night mirror, it is important to adequately distinguish true day from true night conditions so that when daytime prevails the mirror remains in the full brightness condition, yet at nighttime it will be opaque when headlights from a trailing vehicle are incident upon it.
The present invention includes a new and unique control which comprises one photodetector for sensing light incident upon the mirror from the rear, i.e. headlights from the rear, and a second photodetector which takes into account ambient conditions, the circuit being organized and arranged in a new and unique manner to achieve a new and unique form of control for this type of rearview mirror.
A further aspect of the present invention relates to a new and unique organization of various component parts in their assembled relationship in the mirror assembly. This is of particular advantage for several reasons, one of which is that a mirror can be fabricated with convenient, cost-effective fabrication procedures while also resulting in a final construction which is functional, yet sturdy and durable and in which certain operational characteristics can be easily set by the observer.
One specific aspect of the invention involves the organization and arrangement of certain parts for making electrical connection between the transmission plate and a circuit board containing the control circuit.
A further specific aspect of the invention comprises the arrangement of user-operable controls on the mirror for convenient accessibility by the observer.
While the invention is illustrated as connected to an external power supply, it can also be adapted to a self-contained battery operation and wherein a dead battery can be readily replaced.
The foregoing features, advantages and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a preferred embodiment of the invention according to the best mode contemplated at the present time in carrying out the invention.